Method of mass-analyzing body fluid and apparatus therefor

ABSTRACT

A living body fluid analyzing system includes a microdialysis for sending a first solution having an osmotic pressure which is substantially similar to a osmotic pressure of a body fluid into a living body and extracting a second solution from the living body. A first flow passage is provided in which the second solution from the microdialysis flows and a second flow passage is provided which mixes the second solution with an organic solution. Furthermore, there is provided a gas source and a gas flow controller which controls a flow quantity of the gas from the gas source and a third flow passage in which a gas introduced from the gas source flows. An ion source is provided having an orifice for spraying and ionizing the second solution from the second flow passage at an end of the third flow passage, and a mass spectrometer is provided for mass-analyzing the ions sprayed from the orifice.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of mass-analyzing a body fluidand an apparatus therefor. More particularly, it relates to a method ofmass-analyzing a body fluid and an apparatus therefor which, bymass-analyzing each kind of substances contained in a body fluid of anextremely high or low electrical conductivity, allow component analysisof the body fluid to be performed and can be preferably used foridentifying each kind of the substances contained in the body fluid.

2. Description of the Prior Art

As a conventional technique concerning a measuring method foridentifying each kind of the substances contained in the body fluid,there is known a method in which the measurement is performed using anelectrochemical detection method and employing as the criterion anoxidation-reduction potential characteristic of a substance. Also, asanother conventional technique, there is known a component-analyzingmethod that, with the use of the mass spectrometry, allows a substanceto be identified from its mass.

Usually, in the mass spectrometry, an analyte solution such as the bodyfluid, after being ionized, is introduced into a mass spectrometer so asto detect mass of each kind of the substances contained in the analytesolution. As a conventional technique concerning an ionization methodused in the mass analysis of this type, there is known, for example, atechnique disclosed in literatures such as USP-5130538. Thisconventional technique is referred to as an electrospray ionizationmethod. In this method, 2.5 kV or more of high voltage is appliedbetween a metal capillary into which the solution is introduced and acounter electrode, namely, with the high voltage applied to thesolution, the solution is sprayed toward the counter electrode over aspace to which the electric field is applied. As a result, anelectrospray phenomenon occurs, forming a Taylor corn between the metalcapillary and the counter electrode. Then, charged droplets, are sprayedfrom a tip of the Taylor corn.

When an electrical conductivity of the analyte solution falls in therange of 10⁻¹³ to 10⁻⁵ S cm⁻¹ (S=Ω⁻¹), the electrospray ionizationmethod according to the above-described conventional technique enables astable ionization to be performed.

As another conventional technique regarding the ionization method forthe analyte solution, there is known, for example, a technique disclosedin literatures such as JP-A-7-306193. The ionization method according tothis conventional technique is referred to as a sonic spray ionizationmethod. In this method, gas is caused to flow outside the capillarycoaxially therewith and thus the analyte solution Is forced to besprayed from a tip of the capillary, thereby generating the chargeddroplets. Incidentally, it is recognized that quantities of the positiveand negative ions thus generated become maximum when velocity of the gasflow at the tip of the capillary is substantially equal to the sonicvelocity.

Moreover, in the mass spectrometry in which, after the analyte solutionsuch as the body fluid has been ionized, the ionized particles areIntroduced Into the mass spectrometer so as to perform the massanalysis, in the case of mass-analyzing a mixture solution in which manykinds of substances are mixed, it is a common practice to employ thefollowing technique: The substances contained in the mixture solutionare separated from each other using a member such as a liquidchromatograph or a capillary electrophoresis system, and after that, themass analysis is performed using the mass spectrometer.

The conventional technique according to the above-describedelectrochemical detection method is a method in which the measurement isperformed employing as the criterion the oxidation-reduction potentialcharacteristic of a substance. As a result, the conventional techniquehas a problem that an accurate measurement is impossible regarding aliving body and, in particular, regarding a substance such as aneurotransmitter the oxidation-reduction potential of which varies witha lapse of time.

Also, in a conventional technique that uses a non-ion trapmass-analyzing apparatus, no matter which method of the electrosprayionization method and the sonic spray ionization method is employed whenperforming the ionization, in the case of mass-analyzing the body fluidin which many kinds of substances are mixed, the following process isrequired: The body fluid is separated for each kind of the substancesmixed, and after that, the ionization is carried out and then the massanalysis is carried out using the mass spectrometer. The conventionaltechnique, accordingly, necessitates a considerable time for thisseparation and, as a result, has a problem that mass analysis cannot beperformed accurately toward the analyte solution such as the body fluidin which the substances contained vary with a lapse of time and thusvalues of the corresponding masses also vary with a lapse of time.

Also, in the conventional technique that uses the electrosprayionization method in association with the mass-analyzing apparatus, asexplained already, it is difficult to perform the stable ionization ifthe electrical conductivity of the analyte solution falls outside therange of 10⁻¹³ to 10⁻⁵ S cm⁻¹(S=Ω⁻¹). As a result, the conventionaltechnique has a problem that, toward the analyte solution such as thebody fluid having an extremely high electrical conductivity, the massanalysis could not be performed.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the above-describedproblems in the conventional techniques and thus to provide aconfiguration embodying a method of mass-analyzing a body fluid and anapparatus therefor which, even toward the analyte solution in which thesubstances contained vary with a lapse of time and the analyte solutionsuch as the body fluid having an extremely high electrical conductivity,allow the ionization thereof to be performed in a short while, thusmaking it possible to mass-analyze the analyte solution in a shortwhile.

A new recognition has been obtained that an ionization source using thesonic spray ionization method makes it possible to ionize the analytesolution regardless of how high or low the electrical conductivity ofthe analyte solution is. In the present invention, the above-describedproblems have been solved by paying an attention to a combination ofthis recognition and an ion trap mass spectrometer that allows the massanalysis to be performed in a short while.

Namely, according to the present invention, in a method ofmass-analyzing a body fluid, which performs component analysis of thebody fluid, an ionization source according to the sonic spray ionizationmethod is employed as an ionization source, and an ion trap threedimensional quadrupole mass spectrometer is employed as a massspectrometer, and after an analyte solution containing a mixture ofliving body substances is ionized directly by the above-mentionedionization source without being separated for each of the substances,the ions are introduced into the mass spectrometer, therebyaccomplishing the above-described object.

Also, the above-described living body substances are collected as theanalyte solution from a living body with a microdialysis probe, and themass analysis is performed in real time by immediately introducing theanalyte solution into the ionization source from the microdialysis probethrough a flowing passage, and also a volatile organic solvent is addedto the above-described analyte solution in order to promote theionization even further, thereby accomplishing the above-describedobject.

Moreover, in an apparatus for mass-analyzing a body fluid, whichperforms component analysis of the body fluid, an ionization sourceusing the sonic spray ionization method and an ion trap threedimensional quadrupole mass spectrometer are provided, and after ananalyte solution containing a mixture of living body substances isionized by the above-mentioned ionization source without being separatedfor each of the substances, the ions are introduced into the massspectrometer, thereby accomplishing the above-described object.

Also, a microdialysis probe for collecting a body fluid from a livingbody is provided, and the mass analysis is performed in real time byimmediately introducing an analyte solution containing the collectedbody fluid into the ionization source from the microdialysis probethrough a flowing passage, thereby accomplishing the above-describedobject. Furthermore, a configuration for promoting the ionization of theanalyte solution is provided by applying a voltage between an electrode,which is provided in the proximity of a capillary constituting theabove-mentioned ionization source, and the analyte solution so that anelectric field is applied to the analyte solution, and also a member foreliminating contaminants contained in the solution to be analyzed isprovided at the front of an ion-introducing orifice of theabove-mentioned mass spectrometer, thereby accomplishing theabove-described object.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram explaining a mass-analyzing method for detectingsubstances contained in a cerebral spinal fluid by means of amass-analyzing apparatus according to an embodiment of the presentinvention;

FIG. 2 is a diagram explaining a detailed structure of a microdialysisprobe and its operation;

FIG. 3 is a diagram showing a mass spectrum of the cerebral spinal fluidmeasured by the mass-analyzing apparatus according to the embodiment ofthe present invention;

FIG. 4 is a diagram showing a mass spectrum of a dopamine standardmeasured by the mass-analyzing apparatus according to the embodiment ofthe present invention;

FIG. 5 is a block diagram explaining a configuration of themass-analyzing apparatus according to the embodiment of the presentinvention; and

FIG. 6 is a diagram explaining time sequences of measurements performedby a three dimensional quadrupole mass-analyzing apparatus and aquadrupole mass-analyzing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, the detailed description will begiven hereinafter concerning an embodiment of a method of mass-analyzinga body fluid and an apparatus therefor according to the presentinvention. Incidentally, the embodiment of the present inventiondescribed hereinafter is an example that makes it possible to performcomponent analysis of in-brain substances while carrying out massanalysis of a cerebral spinal fluid in real time.

FIG. 1 is a diagram explaining a mass-analyzing method for detectingsubstances contained in a cerebral spinal fluid by means of amass-analyzing apparatus according to an embodiment of the presentinvention. FIG. 2 is a diagram explaining a detailed structure of amicrodialysis probe and its operation. FIG. 3 is a diagram showing amass spectrum of the cerebral spinal fluid measured by themass-analyzing apparatus according to the embodiment of the presentinvention. FIG. 4 is a diagram showing a mass spectrum of a dopaminestandard measured by the mass-analyzing apparatus according to theembodiment of the present invention. FIG. 5 is a block diagramexplaining a configuration of the mass-analyzing apparatus according tothe embodiment of the present invention. FIG. 6 is a diagram explaininga time sequence of a measurement performed by a three dimensionalquadrupole mass-analyzing apparatus and a quadrupole mass-analyzingapparatus. In FIG. 1, FIG. 2 and FIG. 5, the reference numerals denotethe components as designated below: 1, 7 pump, 2, 6 flowing passage, 3microdialysis probe, 4 dialysis membrane, 5 brain, 8 ionization sourcehousing, 9 capillary, 10 orifice, 11 gas-flowing passage 12 massspectrometer, 13 in-brain substances, 101 metallic tube, 102 plate-likemember, 103, 111 orifice, 104 fluoroplastic tube, 105 gas flowcontroller, 106 gas-providing member, 107 screw, 108 insulator, 109,109′ flange, 110 intermediate pressure region, 112 einzel lens, 113electrostatic ion-guide, 114 gate electrode, 115 three dimensionalquadrupole mass analyzer, 116 detector, 117 cable, 122, 123 vacuum pump,124 data processor, 125 high vacuum region.

The mass analysis according to the embodiment of the present inventionIllustrated in FIG. 1 is based on a mass-analyzing method that makes itpossible to perform component analysis of in-brain substances in realtimes while collecting the in-brain substances in the cerebral spinalfluid within the brain 5 of an animal to be inspected. Thismass-analyzing method is carried out by an apparatus that includes ansonic spray ionization source and the mass spectrometer 12 having theorifice 103. The sonic spray ionization source includes the pump 1 forsending out a physiological saline, a Ringer or an artificial cerebralspinal fluid into the flowing passage 2, the microdialysis probe 3connected with the flowing passage 2 and inserted into the brain 5 forsending out the cerebral spinal fluid containing the in-brain substancesinto the flowing passage 6, the pump 7 for injecting a high volatileorganic solvent into the cerebral spinal fluid at a middle point of theflowing passage 6, the ionization source housing 8, the capillary 9, theorifice 10, and the gas-flowing passage 11.

Moreover, the mass spectrometer 12 used in the embodiment of the presentinvention is an ion trap three dimensional quadrupole mass spectrometer(3DQMS). The plate-like member 102 is located just in front of theorifice 103 of the mass spectrometer 12. Also, the metallic tube 101connects the flowing passage 6 with the capillary 9. A voltage forpromoting ionization of the cerebral spinal fluid as a sample is appliedbetween the metallic tube 101 and the ionization source housing 8.Electric potential of the metallic tube 101 is ground potential as shownin FIG. 5. Also, gas such as nitrogen gas is introduced from thegas-flowing passage 11 of the ionization source housing 8. Here,velocity of the gas flow is adjusted so that, at the orifice 10, itbecomes substantially equal to the sonic velocity.

In the above-described embodiment of the present invention, the pump 1sends out a solution such as the physiological saline, the Ringer or theartificial cerebral spinal fluid, the osmotic pressure of which is closeto that of the body fluid, into the flowing passage 2, then sending thesolution into the microdialysis probe 3. Here, the physiological saline,which is 0.9% sodium chloride (NaCl)-water solution (w/w), exhibitssubstantially the same osmotic pressure as that of the body fluid. Also,the Ringer and the artificial cerebral spinal fluid exhibitsubstantially the same osmotic pressure as that of the physiologicalsaline, and in addition to the sodium chloride, they contain salts ofsubstances such as magnesium or potassium.

The dialysis membrane 4 is provided in the proximity of a tip of themicrodialysis probe 3. The microdialysis probe 3 is inserted into thebrain 5 so that a portion of the dialysis membrane 4 comes into contactwith the brain 5. The in-brain substances existing within the brain 5pass through the dialysis membrane 4, then entering the solution whichis sent into the microdialysis probe 3 by the pump 1 and the osmoticpressure of which is close to that of the body fluid. At this time,substances having a large molecular weight, for example, a protein,cannot pass through the dialysis membrane 4, and accordingly do notenter the solution the osmotic pressure of which is close to that of thebody fluid.

The solution, into which the in-brain substances have been dissolved andthe osmotic pressure of which is close to that of the body fluid, isintroduced into the flowing passage 6. The flowing passage 6 is branchedat a middle point thereof. The pump 7, which is provided at the end of aflowing passage branched from the flowing passage 6, introduces a highvolatile organic solvent, for example, methanol, into the flowingpassage 6. The solution the osmotic pressure of which is close to thatof the body fluid is mixed with the methanol, thus being formed as ananalyte solution. The methanol assists vaporization of the analytesolution, thus promoting the ionization thereof. At this time, it isallowable that a branched portion is further provided at theabove-mentioned branched portion of the flowing passage 6 with a valveprovided therebetween, and a minute quantity of acid is introduced fromhere simultaneously while adjusting the quantity to be mixed. The acidassists ionization of the in-brain substances.

The analyte solution formed by the mixture with the organic solvent isintroduced into the fused-silica capillary 9 which is provided in theionization source housing 8 and the tip of which is inserted in theorifice 10. The gas for causing the analyte solution to be sprayed isintroduced into the ionization source housing 8 through the gas-flowingpassage 11, and then the gas flows along an outside periphery of thecapillary 9. Moreover, when the gas flows out into the atmosphere fromthe orifice 10 substantially at the sonic velocity, it sprays theanalyte solution that flows out of the capillary 9.

At this time, it is allowable that the metallic tube 101 is providedbetween the flowing passage 6 and the capillary 9 so as to apply thevoltage between the metallic tube 101 and the ionization source housing8. The application of this voltage, after the analyte solution has beensprayed, allows the ionization to be promoted. However, this ionizationitself is possible without the application of the voltage.

Ions of the in-brain substances, which are generated in the sprayed gas,are introduced into the mass spectrometer 12 through the orifice 103 ofthe mass spectrometer 12, thereby performing the mass analysis thereof.By the way, nonvolatile contaminants are contained in the analytesolution sprayed from the capillary 9. The plate-like member 102 isprovided at the front of the orifice 103 in order to prevent thenonvolatile contaminants from adhering to the surroundings of theorifice 103. For this purpose, an aperture the central axis of which isshifted from that of the orifice 103 is bored In the plate-like member102. Concerning the contaminants contained in the analyte solutionsprayed from the capillary 9, if there exist only a small quantity ofcontaminants, it is allowable not to provide the plate-like member 102.

The above-mentioned embodiment of the present invention makes itpossible to, directly and without using any separation tool, send theanalyte solution containing the cerebral spinal fluid, i.e. a sampleextracted from a living body, into the ionization source and to ionizeand mass-analyze it. Consequently, the embodiment makes it possible tocarry out the mass analysis in real time and with a high timeresolution. Namely, the method presented in the embodiment of thepresent invention, in which the mass analysis is carried out directlywithout using any separation tool, is extremely effective in the use formonitoring living body information that is changing from moment tomoment.

Additionally, in the case of the conventional techniques that use anyseparation tool, the sample is collected from the living body with acertain fixed time interval and is injected into a separation tool so asto be separated, and then the separated substances are measured.Accordingly, it was impossible to carry out the mass analysis in realtime. Also, a result obtained is an average value within a certain fixedtime, and thus the time resolution was found to be no good.

Next, referring to FIG. 2, the description will be given belowconcerning a detailed structure of the microdialysis probe 3 and itsoperation.

As illustrated in FIG. 2, the flowing passage 2 and the flowing passage6 are connected with each other at a tip portion of the microdialysisprobe 3. The dialysis membrane 4 is provided in the proximity of thisconnection portion. The solution the osmotic pressure of which is closeto that of the body fluid flows from the flowing passage 2 to theflowing passage 6 through a portion at which the dialysis membrane 4 isprovided. The vicinity of the dialysis membrane 4 is inserted into thebrain 5. The in-brain substances 13, which exist within the brain 5 andare substances other than the substances having a large molecular weightsuch as a protein, enter the solution such as the physiological salinethrough the dialysis membrane 4, then being sent to the massspectrometer 12 through the flowing passage 6.

The embodiment of the present invention, based on the above-describedconfiguration, makes it possible to perform measurements of cerebralfunctions in real time. Furthermore, the embodiment allows the dissolvedsubstances to be extracted without collecting the body fluid from theliving body, thus making it possible to reduce a burden on the body tobe inspected.

A spectrum illustrated in FIG. 3 is a mass spectrum of a cerebral spinalfluid. The spectrum results from an example in the case where an analytesolution is formed by adding 45% of methanol and 5% of acetic acid.

In the illustrated example, peaks corresponding to masses of GABA,epinephrine and uridine, i.e. neurotransmitters within the brain, areobserved. Also, when representing a molecular weight of a substance by mand its amount of charge by z, a peak for a substance that remains whena water molecule comes off from dopamine and a peak for a substance thatremains when a water molecule comes off from the epinephrine areobserved in the vicinities of values of m/z=136, 166, respectively.

It is based on the reason explained below to be able to identifysubstances for these peaks with the substances that remain when thewater molecule comes off from the dopamine or the epinephrine. Namely,employing, as an analyte solution, a dopamine standard solution that isa 1 μmol/liter dopamine concentration of water solution to which 50% ofmethanol is added, the analyte solution has been measured. The resultantmass spectrum obtained is illustrated in FIG. 4. It can be said that,since the analyte solution is a solution of the pure dopamine, the peaksin the spectrum originate from the dopamine except for the peaksoriginating from the solvents, i.e. the methanol and the water.

A peak for the dopamine itself can be confirmed at a value of m/z=154,and the other peaks have been confirmed. These other peaks, judging fromvalues of its m/z, can be considered as a peak for a substance thatremains when the dopamine is oxidized and thus a hydrogen molecule comesoff therefrom and as a peak for a substance that remains when thedopamine is dehydrated and thus a water molecule comes off therefrom.Meanwhile, as seen already in the spectrum illustrated in FIG. 3, in thespectrum in FIG. 3, too, the peak is observed at the same position asthat of the dopamine from which the water molecule comes off and whichis observed in FIG. 4. Consequently, the peak at the value of m/z=136 inFIG. 3 can be identified as a peak for the substance originating fromthe dopamine. Although not illustrated, the above-mentioned reason isthe same concerning the epinephrine, too.

As described above, even if a substance to be identified has beenaltered by causes such as the oxidation or the dehydration, the use ofthe mass-analyzing apparatus according to the embodiment of the presentinvention makes it possible to recognize an existence of the originalsubstance and, what is more, to recognize relative quantities of aplurality of original substances contained in an analyte solution suchas a body fluid. Also, the use of mass-analyzing apparatus makes itpossible to judge the degree of the oxidation or the dehydration.

On the other hand, when measuring the dopamine with the use of theelectrochemical detection method cited as the conventional technique, itis impossible to perform the measurement thereof except for themeasurement of the dopamine that has not decomposed at all (m/z=154).Accordingly, if a time has elapsed since collection of the sample andthe hydrogen molecule or the water molecule has come off, the value tobe measured varies and thus it becomes impossible to perform theidentification.

Next, referring to FIG. 5, the description will be given belowconcerning a concrete configuration of the mass-analyzing apparatusaccording to the embodiment of the present invention. This embodiment isconfigured by combining the sonic spray ionization source with the3DQMS.

The sonic spray ionization source, as was described referring to FIG. 1,includes the ionization source housing 8, the capillary 9, the orifice10, and the gas-flowing passage 11. FIG. 5 shows that the sonic sprayionization source further includes the gas flow controller 105 providedat a middle point of the gas-flowing passage 11 and the gas-providingmember 106. Moreover, the screw 107 fixes the sonic spray ionizationsource and the plate-like member 102, which is illustrated in FIG. 1 aswell, to the first flange 109 in which the orifice 103 of the 3DQMS 12is provided. The insulator 108, which is located among the ionizationsource housing 8, the plate-like member 102 and the first flange 109,insulates the three components to each other.

The 3DQMS 12 includes the intermediate pressure region 110, which isevacuated by the vacuum pump 122 and formed between the first flange 109and the second flange 109′ having the second orifice 111, and the highvacuum region 125 which is evacuated by the second vacuum pump 123 andin which members such as the mass analyzer are located. Furthermore, theeinzel lens 112, the electrostatic ion-guide 113, the gate electrode114, the three dimensional quadrupole mass analyzer 115 and the detector116 are provided within the high vacuum region 125. An output of thedetector 116, through the cable 117, is sent to the data processor 124such as a personal computer and is processed, thereby being displayed asa graph or the like representing the spectral distribution or beingprinted out.

In the embodiment of the present invention configured described above,the analyte solution containing the in-brain substances is introducedinto the ionization source housing 8 through the flowing passage 6 andthe metallic tube 101. Between the ionization source housing 8 formed ofa metal and the metallic tube 101, it is allowed to apply a high voltageof about—1.2 kV on the side of the ionization source housing 8. This isintended to generate an electric field between the ionization sourcehousing 8 and the metallic tube 101 so that the analyte solution ispositioned in the electric field, as a result, positive ions can beextracted more effectively. Incidentally, it is not necessarily requiredto ground the metallic tube 101. It is sufficient to apply the voltageso that the electric field is applied to the sample solution.

A voltage of +150 V is applied to the first flange 109. Also, aconfiguration of the first flange 109 may be a configuration in which aportion of the orifice 103 is projected on the side of the plate-likemember 102, or may be a plane-like configuration. Although the insulator108 insulates the ionization source housing 8, the plate-like member 102and the first flange 109 to each other, it is allowable to apply adifferent voltage to them each. Also, it is allowable to locate a heateron the plate-like member 102 and heat it.

The sample solution, which have passed through the metallic tube 101, isintroduced into the capillary 9 extending through the fluoroplastic tube104. The tip portion of the capillary 9 is inserted in the orifice 10.Gas such as nitrogen gas or the air is introduced from the gas-providingmember 106 into the ionization source housing 8 through the gas flowcontroller 105 and the gas-flowing passage 11. Flow quantity of the gasis adjusted by the gas flow controller 105 provided at the middle pointof the gas-flowing passage 11. Then, the gas flows out into theatmosphere from the orifice 10 substantially at the sonic velocity andsprays the sample solution that flows out of the capillary 9, therebyionizing under the atmospheric pressure the in-brain substancescontained in the sample solution.

The generated ions pass through the aperture in the plate-like member102 and the orifice 103, and are introduced into the intermediatepressure region 110 evacuated by the vacuum pump 122, then beingintroduced through the second orifice 111 into the high vacuum region125 evacuated by the vacuum pump 123. A voltage of about +160 V, whichis about 10 V higher than the voltage applied to the first flange 109,is applied to the second flange 109′ in which the second orifice 111 isprovided. The ions having passed through the second orifice 111 passthrough the einzel lens 112, the electrostatic ion-guide 113 and thegate electrode 114, then being introduced into the three dimensionalquadrupole mass analyzer 115.

The gate electrode 114, using a voltage applied thereto, permitsincidence of the ions into an ion trap portion from the outside whileaccumulating the ions, and, while measuring the ions, permits emissionof the ions from the ion trap portion to the outside, thus introducingthe ions into the three dimensional quadrupole mass analyzer 115. Theions introduced into the three dimensional quadrupole mass analyzer 115are exhausted while being mass-separated in a direction opposite to thedirection in which the ions had been introduced. Then, the exhaustedions collide with the detector 116, thereby being detected. At thistime, it is allowable to configure the embodiment by equating theion-introduced direction with the ion-exhausted direction. The outputsignal of the detector 116 is sent through the cable 117 to the dataprocessor 124 such as a personal computer and is processed, therebybeing displayed as a graph or the like representing the spectraldistribution or being printed out.

In the embodiment of the present invention, as described above, byemploying the mass spectrometer that includes the three dimensionalquadrupole mass analyzer having the ion trap portion, it is possible toperform the mass analysis concerning a small quantity of sample solutionin a short while and with a high sensitivity.

Next, referring to FIG. 6, the description will be given belowconcerning time sequences of analyses performed by the three dimensionalquadrupole mass spectrometer (3DQMS) employed in the present inventionand a quadrupole mass spectrometer (QMS) in the conventional techniques.

The 3DQMS is an ion trap mass spectrometer, in which a singlemeasurement (1 scan) of a mass spectrum consists of a process ofaccumulating the ions (accumulation) and a process of performing themeasurement. In this measurement, range width of the mass spectrum canbe set freely within a specified range. Accumulation time can also beset freely within a specified range. As the accumulation time is set tobe longer, quantity of accumulated ions can be increased and intensityof measured ions can be heightened. Also, measurement time changes,depending on the set range width of the mass spectrum.

The 3DQMS stores ions the masses of which are within a specified rangewithin the set accumulation time. Next, the 3DQMS expels the stored ionsfrom an ion accumulation unit in the order of increasing or decreasingmasses, then sending them into the detector and performing the massmeasurement. A time for the one scan thereof is short, falling in therange of a few milliseconds to a few hundred milliseconds.

Meanwhile, the QMS in the conventional techniques, which does notnecessitate the process of storing the ions, can perform the singlemeasurement (1 scan) only with the process of the measurement. The QMSpermits only an ion having a specific mass to pass through and sends itinto the detector, thereby separating the ion. Moreover, the QMSchanges, in the order of increasing or decreasing masses, masses of theions that can pass through the QMS, thereby obtaining the mass spectrum.Range width of the mass spectrum in the QMS can be set freely within aspecified range. Also, a time for the one scan depends on the set rangewidth of the mass spectrum, falling in the range of a few hundredmilliseconds to a few seconds. Also, the QMS does not store the ions,and accordingly the ion quantity in the one scan (signal quantity) issmaller as compared with the case of the 3DQMS. This condition forcesthe QMS to performs the measurement for a longer time interval ascompared with the case of the 3DQMS, thus making it necessary tointegrate the mass spectrum over so many scans.

As described above, the QMS in the conventional techniques requires themeasurement for a longer time interval, and what is more, necessitatesan even larger quantity of the sample in comparison with the case ofusing the 3DQMS. However, the living body fluid such as the cerebralspinal fluid, i.e. an object of the measurement performed by theembodiment of the present invention, cannot be collected in largeamounts, and thus there exists a limit to the quantity of the sample.This situation makes it difficult to perform the measurement with theuse of the QMS.

In contrast with this situation, the embodiment of the presentinventions makes it possible to perform the mass analysis in a shortwhile, using a minute quantity of sample. Generally speaking, functionsof the brain are embodied by mutual operations among a plurality ofsubstances. Accordingly, in order to realize the cerebral functions, itis necessary to know ratio of concentrations among respective substancessecreted within the brain. By the way, as illustrated in FIG. 3, theabove-mentioned embodiment of the present invention makes it possible torecognize the ratio of concentrations among the in-brain substances inreal time. Consequently, the embodiment of the present invention makesit possible to perform analysis of the in-brain substances in responseto a change of the living body.

The above-described detailed description concerning the embodiment ofthe present invention has been given in such a manner that theembodiment is able to measure the in-brain substances in the cerebralspinal fluid in real time. The present invention, however, is able toidentify in real time various kinds of substances that are contained inliving body fluids other than the cerebral spinal fluid, such as aspinal fluid, and that vary with a lapse of time. Also, the presentinvention makes it possible not only to perform the real timemeasurement but also to perform measurement of collected samples using abatch processing.

As described above, even toward the body fluid, i.e. an analyte solutionin which the substances contained vary with a lapse of time and whichhas an extremely high electrical conductivity, the present inventionallows the ionization thereof to be performed in a short while, thusmaking it possible to mass-analyze the analyte solution in a shortwhile. As a result, it becomes possible to mass-analyze living bodysubstances, in particular, neurotransmitters in a state in which theyreally are in the living body, although it was impossible for theconventional techniques to perform such type of mass analysis.

What is claimed is:
 1. A mass-analyzing apparatus for a living bodyfluid, comprising: a microdialysis probe for collecting said living bodyfluid from a living body, a first flow passage through which an analytesolution including the living body fluid collected by the microdialysisprobe flows, a second flow passage having a branched portion connectedwith an end portion of said first flow passage, said branched portionmixing the analyte solution with an organic solvent, a third flowpassage through which the analyte solution mixed in said second flowpassage flows, a fourth flow passage for causing a gas to flow aroundsaid third flowing passage, an ion source for spraying and ionizing theanalyte solution from said third flow passage by a high speed gas fromsaid fourth flow passage so as to provide ionized ions, and an analyzingunit for mass-analyzing the ionized ions in real time.
 2. Themass-analyzing apparatus for a living body fluid as claimed in claim 1,further comprising an electrode provided in proximity to said third flowpassage included in said ion source, wherein a voltage is suppliedbetween said electrode and said analyte solution and thereby an electricfield is applied to said analyte solution.
 3. A mass-analyzing apparatusas claimed in claim 1, wherein said microdialysis probe collects livingbody fluid from said living body by sending a solution having an osmoticpressure which is substantially similar to an osmotic pressure of saidliving body fluid into said living body and collects said living bodyfluid from said living body as part of said analyte solution which flowsthrough said first flow passage.
 4. A mass-analyzing apparatus for aliving body fluid, comprising: a first flow passage for flowing a samplesolution containing a sample to be analyzed, a second flow passage forsupplying an organic solution for moving with said sample to be analyzedflowing on said first flow passage, a third flow passage for introducingsaid solutions from said first flow passage and said second flow passageinto an ion source, a ground electrode provided on said second flowpassage and proximate to said third flow passage, said ion sourcespraying said sample solution from a tip of said third flow passage andthereby ionizing it, a gas supply passage provided around third flowpassage, and an analyzing unit for analyzing ions from said ion source.5. The mass-analyzing apparatus for a living body fluid as claimed inclaim 4, a portion of said third flow passage being formed of anelectrically conductive material, said ion source ionizing said samplesolution through an application of a voltage between said gas-supplypassage and said third flow passage.
 6. The mass-analyzing apparatus fora living body fluid as claimed in claim 4, wherein said first flowpassage includes a microdialysis for collecting living body fluid from aliving body as the sample to be analyzed by sending a solution having anosmotic pressure which is substantially similar to an osmotic pressureof the body fluid into said living body and obtaining said samplesolution including said sample to be analyzed from said living body. 7.A living body fluid analyzing system comprising: a microdialysis forsending a first solution having an osmotic pressure which issubstantially similar to an osmotic pressure of a body fluid into aliving body and extracting a second solution from said living body; afirst flow passage in which said second solution from said microdialysisflows; a second flow passage which mixes said second solution with anorganic solution; a gas source; a gas flow controller which controls aflow quantity of the gas from said gas source; a third flow passage inwhich the gas introduced from said gas source flows; an ion sourcehaving an orifice for spraying and ionizing said second solution fromsaid second flow passage at an end of said third flow passage; and amass spectrometer for carrying out mass analysis of ions sprayed fromsaid orifice.
 8. A living body fluid analyzing system as claimed inclaim 7, wherein said microdialysis includes a dialysis membrane.
 9. Aliving body fluid analyzing system as claimed in claim 7, wherein saidsecond flow passage includes a portion which is grounded.
 10. A livingbody fluid analyzing system as claimed in claim 9, wherein said portionof said second flow passage includes an electrode.